Take a rape victim from south London and another from north London and the chances of their attacker being prosecuted could be heavily dependent on where they live.

This "justice by postcode" scenario has proved to be of such concern to the Metropolitan Police that a review has been launched to examine the factors behind such varying clear-up rates.

Overall, figures show one in five reported rapes in London leads to a caution or charge, but the Met is keeping quiet on which boroughs are getting good results and which are falling behind.

The review, to be published by the end of July, also comes against a backdrop of falling rape conviction rates in the city.

It is about how we can find out what they do well so standards are consistent across London

Det Ch Insp Dave Osborn

Det Ch Insp Dave Osborn, who is working on the inquiry, said: "This review is not about the Met failing in rape (investigations) but about looking at good practice and making sure we are not complacent."

The Met's work on rape breaks down into three strands - investigation, victim care and cold case reviews of historic cases.

The review will focus on the investigation side and a look at what has allowed some boroughs to excel, said Det Ch Insp Osborn.

"It is about how we can find out what they do well so standards are consistent across London," he said.

More women are reporting rape because there is more rape

Sandra McNeill, Truth About Rape

In 2001, the Met launched Project Sapphire, billed as the most comprehensive reform programme on rape investigation ever undertaken by the service.

The project, which ran across all London boroughs, aimed to increase the Met's professionalism in the treatment of victims and the way rape allegations were investigated.

Sapphire also aimed to build public confidence in the police's handling of such crimes.

Its success, say police, has resulted in more people coming forward.

'Lost evidence'

Sandra McNeill, from campaign group Truth About Rape group, welcomed the inquiry but was less convinced about its success.

"I get fed up with police saying that the number of rapes being reported is going up but not the number of rapes. More women are reporting rape because there is more rape."

"They rely too heavily on DNA. Police should be detectives. If she [the victim] said she screamed, why not ask the neighbours?" she said.

"In one case from London, officers said they had lost the evidence, which shows they just don't take it as seriously as they should."

Victims of rape drop out at all stages because they are not being respected, supported or believed